Monitoring sports and swimming

ABSTRACT

A data logger for a swimmer which includes an accelerometer, and a GPS unit to sense position and velocity, a heart rate monitor, a controller programmed to manipulate the data and provide a display of the heart rate, lap times, stroke rate etc. The data can be stored or transmitted to a remote computer for use by the coach. The device can also be adapted for other sports.

This invention relates to a method and system for monitoring performancecharacteristics of swimmers and in particular the particular movementswhich contribute to enhanced performance.

BACKGROUND TO THE INVENTION

Monitoring of athletes performance both in training and in competition,is important in the development and implementation of new approachesaimed at improving sporting performance.

The ability to measure and record athlete physiological information andpositional information associated with athlete movement in real-time iscritical in the process of athlete training and coaching. Blood oxygen,respiration, heart rates, velocity, acceleration/force, changes indirection, and position and many other factors are required in eliteathlete training and coaching. The position, movement and forceinformation plays an important role in effective analysis of the athleteperformance, especially for rowers. For example, the stroke frequency,force and synchronization of athletes are critical for the performanceof the rowers in a competition. Currently the stroke information canonly be measured in either dedicated sports laboratories or usingsimulated devices. Reliable analysis of the stroke rate and strokedistance in rowing has been a challenge for a long time due to theavailability of the real scenario data, in particular a high precisionof position, velocity and acceleration data. Existing technologies usedfor this purpose include theoretical studies, video-footage procedure,indoor tank procedure, computer modeling and ergometer studies. Much ofthe equipment is either too heavy, expensive, obtrusive or lessreliable. Therefore, smart real-time monitoring during training andcompetition to help elite athletes to improve their performance andavoid injuries is critical for both athletes and coaches. Anymethodology that would improve the situation would not only bringbenefits to the rower practice, but also to many other sports relatedapplication including both team sports and individual athlete.

U.S. Pat. Nos. 4,984,986 and 5,099,689 disclose measuring systems foroff water rowing apparatus which measure the number of strokes or theforce applied to the machine.

U.S. Pat. No. 6,308,649 discloses a monitoring system for sail boatracing which provides feedback to the crew of such parameters as windspeed and direction boat speed, sail boat comfort parameters, sailshape, line tensions, rudder angle etc.

Some development of monitoring systems has occurred in non water sports.U.S. Pat. No. 6,148,262 discloses a bike mounted sports computerincluding a GPS receiver to provide a mapping facility.

U.S. Pat. No. 5,685,722 discloses swimmers goggles which incorporate atimer and a display. An accelerometer senses the tumble turns to countlaps and the goggles include a strap to sense the pulse of the swimmer.Such head-mounted systems make it difficult to discriminate between themovements of the head and the rest of the body of the swimmer.

Wrist watch type sensors for swimmers have also been proposed as in U.S.Pat. No. 5,864,518 and application 2004/0020856.

Recently proposed swimming loggers prefer a display in the goggles.

U.S. Pat. No. 6,033,228 discloses a device attached to a swimmers waist.The device includes an impeller magnetic device which is able to signalchanges in speed to a visual display worn by the swimmer.

U.S. Pat. No. 5,685,722 discloses a goggle mounted accelerometer anddisplay.

WO/03061779 suggests displaying real time data visually in the gogglesbut does not suggest aural display. This disclosure favors separation ofthe display from the motion sensor which is located preferably on theback with RF transmission to the display. There is a suggestion ofmonitoring pulse rate using a temporal artery and to integrate the wholedevice into one unit on the goggles.

Accelerometers are able to detect changes in acceleration but do notprovide a meaningful measure of velocity.

It is an object of this invention to provide a device for real timemonitoring of swimmers that is useful during a training session and alsofor coaches to carry out detailed analysis after the training session.

BRIEF DESCRIPTION OF THE INVENTION

To this end the present invention provides a data acquisition system foruse in swimming which incorporates

-   -   a) a global position sensor to derive 3 dimensional positioning        data relative to time elapse    -   b) at least one accelerometer to derive acceleration and        velocity data in 3 dimensions    -   c) a microcontroller with a clock to interrogate the global        position sensor preferably at a frequency of at least 1 Hz and        to measure the accelerometer data    -   d) a power supply    -   e) communication means for transmission of global position and        accelerometer data from the microcontroller to a remote computer        device    -   f) the remote computer device being programmed to use the global        position and accelerometer data to provide accurate and        continuous output of parameters such as velocity acceleration        and distance traveled.

This device will provide positional data from the training andcompetition environment and provide both athlete physiological data andperformance data related to the sport.

The movement sensor is an accelerometer combined with a GPS unit tosense instantaneous position and velocity. A GPS receiver transmitter isincluded in the device to derive location and speed parameters.

Preferably physiological sensors are also attached to the athlete andintegrated with the sensor system. Heart rate is the prime parameter tobe measured and this may be sensed using electrical sensors ormicrophones. Respiratory rate is also important and may be measured bysensing the stretching of a chest band or using a microphone and signalrecognition software. Another parameter is arterial oxygen saturationwhich may be measured non invasively by a sensor, placed on an earlobeor finger tip, using pulse oximetry employing an infra red absorptiontechnique. Infra-red spectroscopy may be used for non invasivemeasurement of blood lactate concentrations.

Preferably velocity is derived from the global position sensor and theaccelerometer data is sampled to obtain movement characteristics of thesport being monitored. Preferably the accelerometer data is integratedto derive velocity related movement characteristics and drift is checkedevery second using the output from the global position sensor.

This system provides a platform device which can be used for a widerange of sports simply by providing appropriate software to derive fromthe accelerometer and GPS data, the desired sport parameters such asstride frequency velocity stride length, vertical acceleration, time offthe ground for long jumping and events such as aerial skiing. The systemof this invention can be used in swimming to identify stroke type,turns, and with turns the number of laps and the stroke rate per lap aswell as lap times. Careful analysis of each stroke can show theefficiency and power by comparing the acceleration and decelerationcycles and the effect of breathing cycles. In open water swimming theGPS can also be used to provide an indication of location, direction,and speed relative to the course.

The device of this invention may also include an accelerometer so thattri-athletes who run and swim can obtain accelerometer (pedometer) basedspeed and distance data for the land portion of their activities.Similarly GPS devices may also be included to derive similar distanceand speed data. By adding a magnetometer to the unit on the cyclistpedal cadence can be sensed.

Alternatively pedal cadence can be sensed by a unit on the bike andtransferred to the unit on the cyclist using a radio frequency pickupunit.

The accelerometer information may also be used to determine stroke type,stroke count, turns, lap count, lap times and speed in swimming andstride count, stride length and speed in running and cadence and powerin cycling.

In another embodiment the present invention provides a wrist mountedsensor with a large display screen able to communicate with a secondunit mounted on the swimmers head. Because GPS may not receive signalswhen the device is submerged the GPS unit may be mounted in the unit onthe head and communicates wirelessly with the device on the wrist whenthe wrist is out of the water. Alternatively it is within the scope ofthis invention to modify the GPS polling routine to ensure that basiclocation information can be received within the time interval that thewrist is clear of the water.

This means that the display unit can receive and process the sensor datafor display when required. It is preferred for open water swimming tocombine a GPS sensor with triaxial accelerometers to provide theessential velocity, distance, direction and stroke information. Theaccelerometers in combination with the processor clock provideinformation relating to stroke type, number of strokes per lap, laptimes, turn efficiency and velocity off the wall. The velocitymeasurements from accelerometers tend to drift and the GPS signals areused to correct the velocity measurements in open water. The GPS canalso be used to provide directional and distance information in openwater as well as the same information in running and cycling. For triathletes the accelerometers can also provide stride information and forthe bicycle leg cadence information on the number of pedal revolutions.The central processor can also be in communication with a physiologicalsensor such as a heart rate monitor mounted on the athletes chest.

The quality of the display is an important issue particularly forswimmers. In a preferred aspect the wrist mounted display providesdifferent coloured screens for preprogrammed functions. For example ifthe athlete is attempting to maintain a heart rate within a certain banda first colour indicates that the rate is within the band and a secondcolour indicates that it is too low and a third colour that it is toohigh. In open water swimming one colour may indicate that the swimmer ison course while a second colour may indicate that the swimmer needs tobear to the right and the third colour that the swimmer needs to bear tothe left. In the pool tumble turns provide an opportunity for theswimmer to view a wrist display. As accelerometers allow the turn to beidentified and also indicate the conclusion of a lap, the processor maybe programmed to display on the wrist basic information such the lapnumber and the last lap time. Other information that could be displayedare heart rate and the number of strokes. Such a display is preferablyfor a short time as the swimmer comes off the wall. The display may bebrightly lit for this period and be relatively large. The display canalso be oriented for easy viewing on the wrist when the arms areextended in front of the swimmer which is the usual orientation comingout of a turn.

DETAILED DESCRIPTION OF THE INVENTION

Particular embodiments of the invention will be described.

FIG. 1 is a schematic layout of a data logger used for a rower and arowing shell;

FIG. 2 shows the software output flow diagram for a rowing data logger;

FIG. 3 is a graphical illustration of stroke determined by using GPSdata;

FIG. 4 illustrates the display for a computer screen;

FIG. 5 illustrates the deviation between code and carrier derivedvelocity measurements;

FIG. 6 is a video frame and triaxial accelerometer readings for aswimmer;

FIG. 7 is the core circuit diagram for monitor mounted on a swimmer;

FIG. 8 is the radio transceiver circuit for the monitor of FIG. 7;

FIG. 9 is the sensor circuits for the monitor of FIG. 7.

Recent developments in micro-electromechanical systems (MEMS) technologyhave opened new avenues for the use of high precision lightweightaccelerometers and gyroscopes for new and challenging sportsapplications (eg. characterize rate and length of rowing stroke andstride). MEMS integrate both electrical and mechanical components on asingle chip through extensive research into integrated circuitprocessing technologies. As MEMS accelerometers originated frommonitoring vehicle safety and electronic stabilization, they onlyprovided very low accuracy measurements. However, as micromechanicaldevices are inherently smaller, lighter, and usually more precise thantheir macroscopic counterparts, more and more reliable sensors arebecoming available. Accelerometers measure linear acceleration andgyroscopes measure angular acceleration (pitch, yaw and roll).

Most accelerometers are used concurrently with gyroscopes to form aninertial navigation or “dead reckoning” system. That is where thedeviation from position of a known reference (or starting point) isdetermined by integration of acceleration in each axis over time.

Inertial sensors errors include initial system heading errors,accelerometer scale factor and bias errors. These drifts and biasesinherent in the inertial sensors will cause a misalignment of theplatform and errors in the sensed accelerations, which subsequentlyresults in errors in computed velocities and positions.

The advent of the advanced global navigation satellite systems (GNSS),GPS in particular, has revolutionized conventional precise positioningtechniques. GPS has been made more amenable to a wide range ofapplications through the evolution of rapid static and kinematicmethods, and now even more so with the advent of the On-The-Fly (OTF)technique and most recently network-based RTK techniques such as theTrimble virtual reference station system and Geo++ surface correctionparameter method. Real-time Kinematic (RTK) or single epoch positioningallows for the determination of the integer ambiguities in real-time. Itis therefore not necessary to carry out any static initialization beforeperforming the survey. Due to the small wavelengths of the carrier phasefrequencies (ëL1_(i)Ö19 cm and ëL2_(i)Ö24 cm), the determination ofposition within a specific cycle to a millimetre level by utilizingdifferential carrier phase measurements (i.e. differential techniques)is possible. Most systems statistically determine the most likelysolution for the position of the roving receiver. Virtually, all carrierphase processing algorithms that utilize an OTF technique, rely on thedouble difference carrier phase observables as the primary measurement.A search box is determined within which the position must lie. Allpossible solutions are then assessed and the statistically most-likelycandidate is selected. This procedure is extremely computing intensive,particularly with a large number of satellites.

Regardless of whether the system is for real-time or post-mission use,the algorithm is generally treated the same. Clearly, with real-timeimplementations, data outages, unfavourable observation environments,multipath and cycle slips can severely limit the performance of thesystem. The time for ambiguity resolution can range from a few secondsto several minutes depending on some of the following considerations:

-   -   Use of L1 versus L1-L2 (widelane, L2_(i)Ö86 cm) observable    -   Distance between reference and roaming receivers    -   Number and geometry of satellites    -   Ambiguity search method used and differential atmospheric        conditions    -   Quality of the received signal (multipath effects, code and        carrier phase noise etc.)

Precise detection and removal of cycle slips is essential for thesuccessful use of the OTF kinematic GPS technique. Various cycle slipdetection techniques have been developed in the past decade. Includedare double and triple differencing techniques, comparing the differencebetween adjacent carrier phase and code values (range residual),comparing the adjacent four observables equation, comparing adjacentionospheric residual, the least-squares ambiguity decorrelationadjustment, carrier phase curve fitting, using redundant satellites andusing the raw Doppler values. These methods typically assume a knownstochastic behaviour for un-modeled errors (e.g. noise, multipath,differential atmospheric effects), which if present, will adverselyaffect the performance of the algorithm. None of these techniques can“cure all” kinematic positioning problems. Sometimes a cycle slip may bedetected, but not accurately corrected for. Such instances include aloss of lock, large multipath effects and lower signal-to-noise ratio.This necessitates the combination of two or more of these techniques fora more robust solution.

FIG. 1 illustrates the basic components of a system to monitor boatspeed and an oarsman's heart rate.

The accelerometer provides a PWM output where the duty cycle is relatedto the acceleration. On the rising edge and falling edge of the PWMoutput, a timer value is captured and used to calculate theaccelerometers duty cycle. The firmware also includes an algorithm toadjust for jitter in the PWM period, and for a small amount of drift. Amore detailed algorithm that compensates for temperature drift over timehas been looked at, and will be implemented at a later date.

The impeller pickup uses a Melexis MLX90215 Hall Effect sensor to detectthe rotations of the NK impeller. The MLX90215 is programmed with asensitivity of 100 mV/mT. Output from the sensor is amplified by 100 toincrease the signal amplitude to a usable range. This signal is thensampled using an A/D at 1200 Hz and processed using DSP techniqueswithin the firmware to calculate rotations. Instead of using an impellerto detect boat speed a water flow sensor may be used. One preferredsensor is a micro PCB or silicon based micro fluid flow sensor that usesa heater in combination with a heat sensor that measures the change intemperature of fluid flowing past the heater and sensor to determine thefluid flow rate which in this case is the water flowing past a fixedpoint on the boat hull. This can then be used to measure boat speed.

For competition and race profile analysis it is preferred not to useimpellers or water flow sensors but rely on GPS and accelerometers.

The display device is a handheld Compaq iPAQ™ computer programmed topresent the data in a form that is useful to a coach or rower.

It is preferred that the device have data logging and IrDA transfercapabilities which makes data storage on the unit of slightly lessimportance. However storing data on the unit makes sense as the raw datacan be streamed into the device and the greater processing power of theunit chip allows for flexible software and display development.

The microprocessor is a Hitachi HD64F3672FP which stems from the H8/300Hfamily. Its main features are:

-   -   eight 32-bit registers OR sixteen 16-bit or sixteen 8-bit    -   Serial communication Interface (SCI)    -   10-bit ADC (4 channels)    -   2 k bytes of RAM

The accelerometer unit is powered from a 9 Volt battery, which isregulated down to 5 volts internally. The dimensions of theaccelerometer unit are 25 mm×30 mm×9 mm (smaller that the averagematchbox). The cover needs to be splash proof but importantly the on/offbuttons and start/stop buttons etc must be able to be accessed even whenthe rowers are wearing gloves.

All the chips that have been selected are amongst the smallest availablein their range, the Hitachi HD64F3672FP measures on 12 mm×12 mm, thisincorporates a 64 pin architecture and the ADXL202 measuring only 5 mm×5mm.

FIG. 2 illustrates the output flow from the various sensors namelyimpeller, heart rate monitor, clock, GPS sensor and 3 D accelerometer.Stroke rate and stroke drive to recovery ratio are most convenientlyderived from the accelerometer data while intra stroke velocity,distance per stroke and velocity per stroke are derived from theaccelerometer, GPS and time clock data.

The data for 1 block (by 3 or 4 channels) will be packaged andtransmitted in a single frame. The sampling time for a frame (1 block at150 samples/sec) will be equivalent to 6.6 ms. This data will becombined with block and channel information.

A total of eight bytes is required to transmit one block of data thisincludes the header, two 16-bit channels, Impeller Rotation count andHeart Rate count. The Heart Rate count is only transmitted once asecond, or one in every 150 frames. Heart rate is an output indicatingthe millisecond value from the previous beat or the millisecond of thebeat that occurred during that packet of information. This is used tocalculate instantaneous HR on a beat to beat basis. Alternately thenumber of beats in 15 secs is totalled and then multiplied by 4 to getthe HR. The algorithm then runs on a 5 sec rolling average to smooth thedata. Given that maximum HR will never exceed 250 bpm this means that atmost a beat will occur every 240 ms which is approximately 1 pulse every2 packets of information. Table 1 shows a block of data excluding theframing and network information data. TABLE 1 Byte 1 Frame header(xEE) 2Number of Blocks(4 bits) Number of channels (4 bits) 3 ACC “Y” bits 1-84 ACC “Y” bits 9-16 5 ACC “X” bits 1-8 6 ACC “X” bits 9-16 7 Impellerrotation count (8 bits) 8 Heart rate count (8 bits)

Table 2 illustrates an example of the bit stream for 2 frames. The firstframe containing two 16-bit channels and Impeller Rotation count, andthe second frame containing two 16-bit channels, Impeller Rotation countand Heart Rate count TABLE 2 Data Stream Meaning 0xEE Header Byte 0x13One Block, eg. 3Channels 0xA9 Acc Y Lower Byte 0xEA Acc Y Upper Byte0x46 Acc X Lower Byte 0xC9 Acc X Upper Byte 0x01 Impeller Rotation Count0xEE Header Byte 0x14 One Block, eg. 4Channels 0xA9 Acc Y Lower Byte0xEA Acc Y Upper Byte 0x46 Acc X Lower Byte 0xC9 Acc X Upper Byte 0x01Impeller Rotation Count 0x02 Heart Rate Count

A single unit may be used for each crew member or the heart rate linesfor each crew member can be included with the accelerometer and speeddata to provide a composite set of data. In a multi crew boat each crewmember has a receiver within 2 feet that picks up the heart rate signalfrom the polar heart rate monitor strapped to each crew member. Eachheart rate monitor transmits a uniquely coded signal that is assigned toeach crew member the boat data logger receives the heart rate signalsfor all crew members by cable from the heart rate receivers

A GPS unit may be integrated with the data logger system. This couldcomprise two units, basic unit plus a second unit for GPS. The unitswould share the same serial line and communicate using a networkprotocol. Alternatively the GPS unit could be connected to the basicunit and additional firmware code added to receive and retransmit data.

Inertial navigation systems (INS) may be used to cover the informationgaps of the GPS outages. When the INS approach is used in rowing, therequired sensors need to be small, lightweight, unobtrusive andinexpensive. These requirements can be met when the sensors aremanufactured with MEMS technology. However, due to inherent biases anddrift errors of accelerometers and gyroscopes, the accuracy of thecurrent state-of-the-art MEMS sensors must be accounted for in highprecision rowing tracking. The basic procedure in INS positioningsystems is to process the inertial sensor data. The double integrationof acceleration measurements, cannot be applied due to the loweraccuracy of MEMS sensors. This is because in the double integration,errors accumulate quickly, which soon result in velocity errorscomparable to typical rowing speeds. However, the advantages of the INSsystem include its low cost and high output rate of the movementinformation.

The high precision GPS system can provide high precision velocity andacceleration information (acceleration is the first derivative ofvelocity and second derivative of displacement). However the GPS systemis normally bulky, expensive and provides a low output rate and highpower consumption. To solve these problems, an integrated system takesadvantage of both low-cost GPS and MEMS sensors to provide highperformance capabilities. MEMS sensors are used to provide precise, highrate (say 200 Hz), low cost, low volume, low power, rugged, and reliablegeo-positioning while low-cost GPS is used for high frequency systemcalibration (say 5-20 Hz) a lower frequency (1 Hz) is preferred forcalibrating the inertial sensors to conserve battery power. It combinesmeasurements from a GPS OEM board and subsequently GPS chip withinertial measurement units from a combination of three MEMS gyroscopesand accelerometers (say Analog Devices).

A 1 Hz GPS receiver is the minimum frequency that is practical andideally a 2-5 Hz system is preferred. With a 1 Hz receiver accuratevelocity and distance measurements can be obtained but sampling theaccelerometer data is needed to obtain stroke rate and intra-strokecharacteristics. The accelerometer data could be integrated to getintra-stroke velocity but drift would need to be checked every secondusing the output from the GPS receiver.

The carrier smoothing procedure will be used to improve the accuracy ofthe low-cost GPS pseudo range measurements. Carrier phase smoothing is aprocess that the absolute but noisy pseudo range measurements arecombined with the accurate but ambiguous carrier phase measurements toobtain a good solution without the noise inherent in pseudo rangetracking through a weighted averaging process. A Kalman filtering systemwill be designed to integrate the two system measurements.

FIG. 3 presents the stroke signals captured using geodetic type GPSreceivers and post-processing with the kinematic differential GPStechnique. It is demonstrated that the signals captured provide a clearpicture of the rowing stroke phases as described above. In thisparticular stroke, the graph indicates that the rower has problem inharmonizing his stroke cycle by using too much time in the catch insteadof the driver.

The software can display the derived information on a computer screenand combine it with video data of the same event as illustrated in FIG.4. The screen may display time and distance information as well asvelocity and stroke rate and can also display the graphical signalsderived from accelerometer and GPS signals.

To evaluate the accuracy of the GPS carrier phase receiver, two GPSreceivers were mounted on the same rowing boat simultaneously. The basestation is located on the bank of a river which is about 1˜2 km awayfrom the course of the boat trial. The baseline solutions from each ofthe rowing antennas were processed independently from the base stationusing the PPK technique. The independent baseline length between the tworoving receivers was then calculated and compared with the resultmeasured using a surveying tape. This baseline length is considered as a“ground truth” (3.57 m in our case).

RTK GPS has been proved to be able to provide high precision positioningin river environment. However, there are a number of factors that needto be taken into consideration:

-   -   Multipath effects: The antenna being positioned near the water        surface could potentially be prone to large multipath error.        This effect can be up to 5 cm for carrier and 5 m for code        measurements respectively.    -   Signal obstruction/satellite visibility: The GPS antenna is        installed in a constricted space in a racing boat, it is        therefore unavoidable that the movement of the athlete will        block the GPS signals at some time to an elevation angle of        approximately 70 degrees. This may potentially cause severe        signal obstruction problems and loss of GPS solutions.    -   Obtrusion: Ideally the presence of any instrument should not        cause direct visual or physical impact on the athlete,        therefore, the size and height of the antenna is a primary        consideration.

The “fixed baseline length” and external check methods are used.Reliable mounting of the GPS receiver is required. If we assume that theaccuracy of the position to one GPS rover is the same as to the other,then, from the simple (Least Squares Adjustment) error propagation law,the accuracy of the position of the kinematic GPS measurement (for asingle baseline) can be estimated as 0.0027 m (0.0038 m/sqrt(2)). A fewmillimetre accuracy of the river height was achieved in a three(consecutive) day trial. Given the closeness of the antenna and thereflective nature of the water surface, the performance of the PPK GPSpresents consistent results.

The velocity determined from the GPS position and time information usesthe following first-order central difference procedure.${{Velocity}( \upsilon_{T} )} = {\frac{{P( {T + {\Delta\quad T}} )} - {P( {T - {\Delta\quad T}} )}}{2\quad\Delta\quad T} = \frac{\Delta\quad P}{2\quad\Delta\quad T}}$

where ν_(T) is the velocity of the boat (at time T) determined from PPKGPS solution, ΔP=P(T+ΔT)−P(T−ΔT) is the plane distance travelled betweentime T₁ and T₂ and ΔT=T₂−T₁.${{\Delta\quad P} = \sqrt{( {N_{2} - N_{1}} )^{2} + ( {E_{2} - E_{1}} )^{2}}},$where E and N are the Easting and Northing coordinates of the GPS units.The subscripts “1” and “2” indicate that position derived from unit 2and unit 1 respectively. The accuracy of the velocity (σ_(ν)), can thenbe roughly estimated through the following formula (using the errorpropagation law):$\sigma_{\upsilon} = {{\frac{1}{\sqrt{2}\Delta\quad T}\sigma_{P}} = {{\frac{1}{\sqrt{2} \times 0.1} \cdot 0.0027} \approx {0.02\quad m\text{/}s}}}$

Where σ_(P) is the positional accuracy and σ_(P)=0.0027 m as determinedpreviously.

FIG. 5 shows the differences in velocity determined simultaneously fromthe code and the carrier measurements. Assuming the carrier velocity tobe accurate (ie ground truth), the code derived velocity has an averageaccuracy in the order of ˜0.03 m/s. The results confirm that theaccuracy of 0.1 m/sec claimed by the manufacturer is correct for morethan 95% of observations.

The data logger assembly is fitted to a rowing shell in a stablelocation with a relatively clear view of the sky. Relative motion of theathlete or boat is measured using three dimensional accelerometer at 100hHz and position and velocity using GPS at 10 Hz. The device suppliestiming information with the measured signals using an internal crystalcorrected clock and a GPS derived 1 Hz pulse. The timing is accurate to0.1 sec per hour. An internal heat rate monitor pickup receives pulsesfrom a coded polar heart rate monitor/transmitter and stores these witha resolution of 1 beat a minute within a range of 0 to 250 beats/minuteupdated at 1 Hz. The device is powered by a battery sealed into the unitand is rechargeable via an RS232 port. Recording battery life is 6 hoursand 1 month in sleep mode. The single universal port allows recharging,connecting an RF module, connecting an external GPS antenna, connectingthe external heart rate receiver and to connect a serial cable to senddata to the hand held computer device. The device can be fitted into aflexible package of a size approximately 100 mm×70 mm×50 mm and weighsless than 250 g and is buoyant and water resistant. The package iscoloured to reduce heating from incident sunlight.

The device can be adapted to detect strokes and turns in swimming asshown in FIG. 6. Analysis of the signals from the 3 axes of theaccelerometer allows coaches to derive information as detailed as strokeformation and turn efficiency.

FIGS. 7 to 9 illustrate the circuitry used in further embodiment of theinvention.

FIG. 7 shows the core circuitry centred on the micro controller 20. Themicro controller is preferably an 8 bit Atmel AT mega 128 microcontroller. The micro controller can be programmed and can store dataand is provided with a 256 megabyte flash memory 27. The USB port 22 ispreferably a Silicon Technologies USB to UART data transfer CP 2101 andallows data to be down loaded to a personal computer for furtheranalysis and storage and also allow the battery to be charged by way ofthe battery charger 31 which in turn is connected to the power supply32. The microcontroller functions are actuated by the tactile switches23 which allows the user to navigate through the device menu. Themicrocontroller displays outputs on the LCD display 35 and also providesa backlight display 36. As shown in FIG. 8 the monitor includes a 2.4GHz transmitter and receiver 40 so that data can be transmitted andreceived. The transmitter and receiver 40 is preferably a GFSKtransceiver nRF2401 sold by Nordic Semiconductor. The output power andfrequency channels are programmable using a 3 wire serial interface. TheGPS unit is an iTRAX 03 by Fastrax with 12 channels and an update ratebelow 5 Hz with a 1 Hz default rate.

The sensor circuits shown in FIG. 9 are the core components of the realtime clock 41 the three axis accelerometer 43. A single externaltransistor may be used to lower the scale factor and an externalcapacitor is used to set the bandwidth.

The micro controller in the swimming monitor is programmed with a set ofalgorithms to process the raw data from the sensors. The algorithmsfilter the raw data with a low pass filter. The aim is to use slowerchanging orientation information from the accelerometers rather thanquickly changing real accelerations. The algorithm looks for peaks andtroughs on each filtered sensor trace. Strokes are defined ascombinations of peaks and troughs—each stroke type has a specificcombination with a specific set of rules. Once locked on to a particularstroke type then look first for that stroke type next. Initially looksfor freestyle first.

Freestyle

-   -   ignores small peaks/troughs    -   requires up/down accelerometer>0    -   requires a sideways accelerometer peak followed by a trough—each        peak/trough is a stroke    -   looks for several strokes in a row to lock on

Backstroke

-   -   ignores small peaks/troughs    -   requires up/down accelerometer to be less than 0    -   requires a sideways accelerometer peak followed by a trough—each        peak/trough is a stroke    -   looks for several strokes in a row to lock on

Butterfly

-   -   consists of two peaks—one higher than the other    -   looks for several fwd/back peaks in a row to lock on—first must        be high, next low, next high etc    -   peaks must be spaced appropriately    -   high peaks should be equally spaced, low peaks likewise    -   high peaks should be equal magnitude, low peaks likewise    -   highest up/down acc peak in the area must be large enough    -   lowest up/down acc peak in area must be significantly less than        highest

Breaststroke

-   -   uses troughs in fwd/back acceleration    -   two quick troughs and a gap    -   looks for several troughs to lock on    -   sufficient trough spacing    -   time between troughs ½ and ¾ should be close    -   time between toughs ⅔ and ⅘ should be close    -   up acc must be >0

There is a fourth type of stroke which is the dolphin kick.

Starts/turns/Finishes

A state variable keeps track of the current lap state. There are 3possible states:

-   -   Waiting for a start    -   Progress during the lap    -   Possible end of lap

Waiting for Start

When a stroke is detected in this state look backwards for the start.Since stroke detection requires several strokes in a row (depending onthe stroke type) then we are likely to be a fair way down the pool atthis stage, particularly after a block start and a few dolphin kicks(these are ignored for start purposes—there has to be several of theregular stroke types in a row before checking for a start).

-   -   After the first stroke look at rate-of-change peaks. If there is        only one, or the highest is large enough, then we have a start        at the highest point.    -   If the above didn't succeed then look for a large swing in z        (up/down acc) in the time before the first stroke—this is        defined as a peak >0 g preceded by a trough <0 g and with        sufficient difference between the two. The start is then the low        fwd/back trough which is close to the highest rate-of-change in        the region.    -   If neither of the above get a result then the start is a fixed        time before the start of the first stroke.

State then changes to . . .

Progress During the Lap

After being in this state for sufficient time, watch for turns or end oflap

-   -   First look for low fwd/back acc readings either side of the end        of the last stroke. If the lowest trough before the end of the        last stroke is sufficiently greater than the lowest trough after        then change state to “Possible end of lap”    -   If above wasn't successful then look for a large vertical        accelerometer swing. Again look either side of the end of the        last stroke. This time search for a z-axis high to low change to        change state to “Possible end of lap”

Within the time it is also possible to change state but only if enoughtime has elapsed with no sign of a new stroke.

End of Lap Detection

At next stroke look back from the start of the last stroke for the endof lap:

-   -   A large swing in z (as above)    -   Or a large rate-of-change (as above)    -   Or the lowest fwd/back acc reading    -   Or a point a fixed time period back

Also look for the finish of a set of laps.

This is done by looking for the first point with “zero” rate-of-changewhich is defined as a short period with all rate-of-change results (iefor every point) sufficiently low. If this is found and there are nostrokes for a while then end of set is assumed to be at the beginning ofthe “zero” rate-of-change period.

A display is mounted in a water proof enclosure in a visible location sothat the athlete can view summary information such as stroke ratedistance and heart rate. An easily accessible button on the display unitstarts the data recording. As soon as the device is switched onrecording begins. The coach may take the device after the event and loadthe data into a personal computer to view the data graphically orcombine it synchronously with video footage.

The device may be attached near the small of the back. An extension GPSaerial runs from the device to the shoulders, but mounting on the wristor head is also possible. A separate GPS unit may be mounted on the headto improve reception and the microcontroller, accelerometers and displaymay be mounted on the wrist or arm.

The RF module enables the real time data to be transmitted to theCoach's wireless enabled PC via a blue tooth connection. Alternativelythe data may simply be uploaded after the event.

The advantages of the swim monitor of this invention are:

-   -   The device can give feedback both in real-time and        post-training.    -   The real-time feedback to the swimmer may be via a variety of        methods:        -   Aural via an ear-piece        -   Visual via a ‘heads-up’ display on the goggle        -   Visual via an LCD panel on the device        -   Visual via a remote display panel either in the pool or            adjacent to it.    -   If the preferred real-time feedback is used, some additional        circuitry incorporating an FM receiver may be used to allow a        coach to talk to the swimmer via the device.    -   The real-time feedback would likely be delivered at the start of        a new lap and would give key results about the previous lap. The        results may include:        -   Average velocity        -   Number of strokes        -   Number of laps completed    -   A further enhancement of the system would be to add an MP3        player or FM receiver to the device so the swimmer may be        entertained.    -   The device may also include pulse counters taking advantage of        the temple mounting for deriving heart rate    -   For tri-athletes the device may include accelerometers or GPS        units to derive speed and distance and stride length data for        the land based activities    -   The post-training display may be on a standard PC. It would show        summary graphs such as ‘velocity vs time’ and ‘stroke-rate vs        time’ for the entire session. It would also be able to calculate        bio-metric efficiencies such as distance per stoke. The user is        able to zoom into a section of the graph to obtain information        about each stroke, enabling the swimmer to gain information        about how bio-metric improvements may be made.

Those skilled in the art will realize that the invention may beimplemented in a variety of embodiments. A variety of sensors may alsobe used to gather data applicable to the event. It will also beappreciated that the logger unit is small and adaptable enough to befitted to any athlete or sporting equipment where accelerometer dataprovides useful performance information for coaches and athletes.

1. A data acquisition system for use in swimming events whichincorporates a) a global position sensor to derive three dimensionalpositioning data relative to time elapse b) at least one accelerometerto derive acceleration and velocity data in three dimensions c) amicrocontroller with a clock to interrogate the global position sensorand to collect the accelerometer data d) a power supply e) communicationmeans for transmission of global position and accelerometer data fromthe microcontroller to a computer device f) the computer device beingprogrammed to use the global position and accelerometer data to provideaccurate and continuous output of parameters such as velocityacceleration and distance traveled.
 2. A data acquisition system asclaimed in claim 1 in which velocity is derived from the global positionsensor and the accelerometer data is sampled to obtain movementcharacteristics in swimming
 3. A data acquisition system as claimed inclaim 1 wherein the accelerometer data is integrated to derive velocityrelated movement characteristics and drift is be checked every secondusing the output from the global position sensor.
 4. A data acquisitionsystem as claimed in claim 1 wherein an inertial navigation system basedon the accelerometer data is used to determine position when the GPSsystem is unable to receive data.
 5. A data acquisition system asclaimed in claim 1 which includes a display screen.
 6. A dataacquisition system as claimed in claim 5 in which the global positionsensor is located in a separate unit to the micro controller and thedisplay.
 7. A data acquisition system as claimed in claim 6 in which theglobal position sensor is adapted to be mounted on the swimmers head andthe display unit is adapted to be mounted on the swimmers wrist
 8. Adata acquisition system as claimed in claim 1 which also includes aphysiological sensor.
 9. A data acquisition system as claimed in claim 6in the physiological sensor is a heart rate monitor.